Android中利用ViewHolder优化自定义Adapter的写法(必看)

2024-02-25 12:38:03 43

最近写Adapter写得多了，慢慢就熟悉了。

用ViewHolder，主要是进行一些性能优化，减少一些不必要的重复操作。（WXD同学教我的。）

具体不分析了，直接上一份代码吧：

publicclassMarkerItemAdapterextendsBaseAdapter
{
privateContextmContext=null;
privateListmMarkerData=null;

publicMarkerItemAdapter(Contextcontext,ListmarkerItems)
{
mContext=context;
mMarkerData=markerItems;
}

publicvoidsetMarkerData(ListmarkerItems)
{
mMarkerData=markerItems;
}

@Override
publicintgetCount()
{
intcount=0;
if(null!=mMarkerData)
{
count=mMarkerData.size();
}
returncount;
}

@Override
publicMarkerItemgetItem(intposition)
{
MarkerItemitem=null;

if(null!=mMarkerData)
{
item=mMarkerData.get(position);
}

returnitem;
}

@Override
publiclonggetItemId(intposition)
{
returnposition;
}

@Override
publicViewgetView(intposition,ViewconvertView,ViewGroupparent)
{
ViewHolderviewHolder=null;
if(null==convertView)
{
viewHolder=newViewHolder();
LayoutInflatermInflater=LayoutInflater.from(mContext);
convertView=mInflater.inflate(R.layout.item_marker_item,null);

viewHolder.name=(TextView)convertView.findViewById(R.id.name);
viewHolder.description=(TextView)convertView
.findViewById(R.id.description);
viewHolder.createTime=(TextView)convertView
.findViewById(R.id.createTime);

convertView.setTag(viewHolder);
}
else
{
viewHolder=(ViewHolder)convertView.getTag();
}

//setitemvaluestotheviewHolder:

MarkerItemmarkerItem=getItem(position);
if(null!=markerItem)
{
viewHolder.name.setText(markerItem.getName());
viewHolder.description.setText(markerItem.getDescription());
viewHolder.createTime.setText(markerItem.getCreateDate());
}

returnconvertView;
}

privatestaticclassViewHolder
{
TextViewname;
TextViewdescription;
TextViewcreateTime;
}

}

其中MarkerItem是自定义的类，其中包含name，description，createTime等字段，并且有相应的get和set方法。

ViewHolder是一个内部类，其中包含了单个项目布局中的各个控件。

单个项目的布局，即R.layout.item_marker_item如下：

官方的APIDemos中也有这个例子：

packagecom.example.android.apis.view中的List14：

/*
*Copyright(C)2008TheAndroidOpenSourceProject
*
*LicensedundertheApacheLicense,Version2.0(the"License");
*youmaynotusethisfileexceptincompliancewiththeLicense.
*YoumayobtainacopyoftheLicenseat
*
*http://www.apache.org/licenses/LICENSE-2.0
*
*Unlessrequiredbyapplicablelaworagreedtoinwriting,software
*distributedundertheLicenseisdistributedonan"ASIS"BASIS,
*WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
*SeetheLicenseforthespecificlanguagegoverningpermissionsand
*limitationsundertheLicense.
*/

packagecom.example.android.apis.view;

importandroid.app.ListActivity;
importandroid.content.Context;
importandroid.os.Bundle;
importandroid.view.LayoutInflater;
importandroid.view.View;
importandroid.view.ViewGroup;
importandroid.widget.BaseAdapter;
importandroid.widget.TextView;
importandroid.widget.ImageView;
importandroid.graphics.BitmapFactory;
importandroid.graphics.Bitmap;
importcom.example.android.apis.R;

/**
*Demonstrateshowtowriteanefficientlistadapter.Theadapterusedinthisexamplebinds
*toanImageViewandtoaTextViewforeachrowinthelist.
*
*Toworkefficientlytheadapterimplementedhereusestwotechniques:
*-ItreusestheconvertViewpassedtogetView()toavoidinflatingViewwhenitisnotnecessary
*-ItusestheViewHolderpatterntoavoidcallingfindViewById()whenitisnotnecessary
*
*TheViewHolderpatternconsistsinstoringadatastructureinthetagoftheviewreturnedby
*getView().Thisdatastructurescontainsreferencestotheviewswewanttobinddatato,thus
*avoidingcallstofindViewById()everytimegetView()isinvoked.
*/
publicclassList14extendsListActivity{

privatestaticclassEfficientAdapterextendsBaseAdapter{
privateLayoutInflatermInflater;
privateBitmapmIcon1;
privateBitmapmIcon2;

publicEfficientAdapter(Contextcontext){
//CachetheLayoutInflatetoavoidaskingforanewoneeachtime.
mInflater=LayoutInflater.from(context);

//Iconsboundtotherows.
mIcon1=BitmapFactory.decodeResource(context.getResources(),R.drawable.icon48x48_1);
mIcon2=BitmapFactory.decodeResource(context.getResources(),R.drawable.icon48x48_2);
}

/**
*Thenumberofitemsinthelistisdeterminedbythenumberofspeeches
*inourarray.
*
*@seeandroid.widget.ListAdapter#getCount()
*/
publicintgetCount(){
returnDATA.length;
}

/**
*Sincethedatacomesfromanarray,justreturningtheindexis
*sufficenttogetatthedata.Ifwewereusingamorecomplexdata
*structure,wewouldreturnwhateverobjectrepresentsonerowinthe
*list.
*
*@seeandroid.widget.ListAdapter#getItem(int)
*/
publicObjectgetItem(intposition){
returnposition;
}

/**
*Usethearrayindexasauniqueid.
*
*@seeandroid.widget.ListAdapter#getItemId(int)
*/
publiclonggetItemId(intposition){
returnposition;
}

/**
*Makeaviewtoholdeachrow.
*
*@seeandroid.widget.ListAdapter#getView(int,android.view.View,
*android.view.ViewGroup)
*/
publicViewgetView(intposition,ViewconvertView,ViewGroupparent){
//AViewHolderkeepsreferencestochildrenviewstoavoidunneccessarycalls
//tofindViewById()oneachrow.
ViewHolderholder;

//WhenconvertViewisnotnull,wecanreuseitdirectly,thereisnoneed
//toreinflateit.WeonlyinflateanewViewwhentheconvertViewsupplied
//byListViewisnull.
if(convertView==null){
convertView=mInflater.inflate(R.layout.list_item_icon_text,null);

//CreatesaViewHolderandstorereferencestothetwochildrenviews
//wewanttobinddatato.
holder=newViewHolder();
holder.text=(TextView)convertView.findViewById(R.id.text);
holder.icon=(ImageView)convertView.findViewById(R.id.icon);

convertView.setTag(holder);
}else{
//GettheViewHolderbacktogetfastaccesstotheTextView
//andtheImageView.
holder=(ViewHolder)convertView.getTag();
}

//Bindthedataefficientlywiththeholder.
holder.text.setText(DATA[position]);
holder.icon.setImageBitmap((position&1)==1?mIcon1:mIcon2);

returnconvertView;
}

staticclassViewHolder{
TextViewtext;
ImageViewicon;
}
}

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setListAdapter(newEfficientAdapter(this));
}

privatestaticfinalString[]DATA=Cheeses.sCheeseStrings;
}

其中布局：

以上这篇Android中利用ViewHolder优化自定义Adapter的写法(必看)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持毛票票。

Android中利用ViewHolder优化自定义Adapter的写法(必看)

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